1. Field of the Invention
The invention relates to optical communication equipment and, more specifically, to micro-electromechanical devices for use in such equipment.
2. Description of the Related Art
Optical communication equipment often employs micro-electromechanical systems (MEMS). A typical MEMS system may include an array of micro-machined mirrors, each mirror individually movable in response to an electrical signal. Such an array may be employed as an element of an optical cross-connect. In operation, at least one mirror in the array receives a beam of light. The beam is reflected from the mirror and can be controllably redirected to a different location by rotating the mirror. More details on the principle of operation and methods of manufacture of MEMS devices including mirror arrays may be found, for example, in commonly assigned U.S. Pat. No. 6,201,631, the teachings of which are incorporated herein by reference.
One problem with prior art MEMS devices is related to manufacturing such devices. During fabrication, two pieces, e.g., wafers, which are used to form the MEMS device must be accurately aligned to properly position the actuating electrodes with respect to the corresponding mirror. Such alignment may be difficult to achieve for relatively small mirrors and/or mirror arrays having a relatively large number of mirrors.
Another problem with prior art MEMS devices is referred to as “snap-down.” More specifically, when the voltage applied to an actuating electrode in such device approaches a critical value, the tilt angle of the mirror begins to increase rapidly and nonlinearly with the voltage. This behavior may cause a collision of the mirror against the electrode and/or wafer, damaging the mirror and rendering the MEMS device inoperable.